optimize dk.sh, support containers with sh in

dk.sh

@@ -1,39 +1,40 @@
 #!/bin/sh
 
-# this script provides access to scratch-based containers by temporary copy busybox in.
-# removes all of this on exit
+# this script provides access to scratch-based containers ot any other container without shell
+# by temporary copy busybox in. removes all of this on the exit
+
+# check if sh is already available
+if docker exec -it "$1" sh -c ls 1>/dev/null 2>/dev/null; then
+    # check for available shells
+    for shell in bash zsh ash sh; do
+        if docker exec -it "$1" $shell -c ls 1>/dev/null 2>/dev/null; then
+            docker exec -it "$1" $shell
+            exit 0
+        fi
+    done
+    exit 1
+fi
 
 id="$$" # randomize file names to prevent collisions if run multiple times
 
 # copy busybox into running container as /busybox.<random>
-docker run -d --rm --name=bbox busybox:latest sleep 10 1>/dev/null 2>/dev/null
-docker cp bbox:/bin/busybox .
-docker cp ./busybox "$1":/busybox.${id}
+docker run -d --rm --name=bbox busybox:stable-musl sleep 10 1>/dev/null 2>/dev/null
+docker cp bbox:/bin/busybox .  1>/dev/null 2>/dev/null
+docker cp ./busybox "$1":/busybox.${id}  1>/dev/null 2>/dev/null
 rm -f ./busybox
 
 # install busybox inside the container
 docker exec -u 0 -it "$1" /busybox.${id} sh -c "
-export "PATH=/busybin.${id}"
+export PATH=/busybin.${id}
 /busybox.${id} mkdir /busybin.${id} 2>/dev/null
 /busybox.${id} --install /busybin.${id}
 "
 
-# make shell script with busybin path and copy it in
-script="
-export "PATH=/busybin.${id}"
-sh
-"
-echo "$script" > sh.${id}
-chmod +x sh.${id}
-docker cp sh.${id} "$1":/sh.${id}
-rm -rf sh.${id}
-
 # invoke container shell
-docker exec -it "$1" /busybox.${id} sh -c /sh.${id}
+docker exec -it "$1" /busybox.${id} sh -c "export PATH=/busybin.${id}; exec sh"
 
 # cleanup temp files on exit
 docker exec -u 0 -it "$1" /busybox.${id} sh -c "
-echo cleaning...
 /busybox.${id} rm -rf /busybin.${id}
 /busybox.${id} rm -f /sh.${id}
 /busybox.${id} rm -f /busybox.${id}